Men's Carhartt LS T-shirt 2XL Gray CARHARTT on Sleeve & Upper Back Cotton Blend

Brand is Carhartt Men's LS t-shirt Size 2XL, color is gray Solid color with Carhartt on sleeve & upper back Material is a cotton blend of 90% cotton, 10% polyester Chest: 27" (68.58 cm) flat across back underarm to underarm Length: 32" (81.28 cm) neckline to hemline Sleeve length: 23" (58.42 cm) from shoulder seam to end of sleeve This shirt is pre-owned, but has a dark smudge on back side below the word Carhartt, I am not sure if it is a stain or what it would be